In a typical four-stroke internal combustion engine, the piston rings are freely rotatable within grooves in the pistons. However, in a two-stroke engine, it is important to lock the piston ring in the piston groove, so that the piston ring will not rotate relative to the piston. If the piston ring is able to rotate freely within the groove in the piston of the two-stroke engine, one or both of the ends of the split ring could expand outwardly into an open scavenging port, causing the ring to break off and jam between the piston and cylinder wall, resulting in severe damage to the engine.
In the past, the conventional manner of locking the piston ring to the piston in a two-stroke engine was to press a small diameter locating pin into a radially extending hole in the bottom of the groove of the piston, and a notch, cut into the piston ring end gap, engaged the projecting end of the pin. With this construction, it was found that failure could occur when the piston was exposed to high compression temperatures that act to soften the piston material surrounding the locating pin, resulting in the pin becoming loose. This problem was compounded by side loads imparted by the ring acting against the pin during operation of the engine. Thus, the combination of high temperatures along with side pounding loads often resulted in breakage of the pin, or the pin being pounded deeper into the piston, until it no longer protruded into the ring gap. When this condition occurred, the piston ring could then rotate freely and the ends of the split ring could deflect outwardly into an open scavenging port to cause severe engine damage, as previous described.